Delaying the closing of an intake valve when an engine piston compression rises from a bottom dead center is known to be effective for controlling the ignition timing of fuel in a Miller cycle or premixed combustion (PCI combustion).
For example, a variable valve driving device disclosed in Japanese Patent No. 2970388 has been suggested as a device capable of changing the closing timing of intake valves.
Japanese Patent No. 2970388 discloses a variable valve driving device including a plunger that is driven by a cam in a cylinder head of an engine, an actuator for pressing an intake valve communicating with a plunger chamber pressurized by the plunger in the valve opening direction, a hydraulic pump for supplying hydraulic pressure into the plunger chamber, a hydraulic chamber provided between a retainer of the intake valve and the cylinder head that presses the intake valve in the valve closing direction, switching means inserted into a channel which links the plunger chamber to the hydraulic chamber, and an accumulator connected between the hydraulic chamber of the channel and the switching means.
In such variable valve driving device, when the intake valve is lifted, the plunger chamber and hydraulic chamber are disconnected by the switching means, the actuator is driven by a hydraulic pressure of the plunger chamber which is pressurized by the plunger driven by the cam, and the intake valve is opened. The hydraulic pressure of the hydraulic chamber, which is pressurized as the intake valve is opened, is accumulated in the accumulator. Where the plunger chamber and hydraulic chamber are linked by the switching means in the lifting process of the intake valve, the hydraulic pressure created by the pressurization of the plunger chamber and the hydraulic pressure accumulated in the accumulator are supplied into the hydraulic chamber and the intake valve is closed.